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102 ARTURIA – MOOG MODULAR V 2.6 – USER’S MANUAL
The complete cycle of a wave form (sawtooth) = one period
Oscillator synchronization: the second is synchronized on the first one
In the image above, oscillator2 is synchronized with the first, and then tuned to a frequency
with double the tonality.
The noise module: the noise signal spectrum possesses all frequencies at the same volume.
For this reason, the noise module is used to create different noises like the imitation of wind or
a breath, or even special effects. White noise is the richest of noises. Pink noise is also
commonly present on synthesizers. It is not as rich in high frequencies as white noise, having
received a low pass filtering.
Also, note that the audio output of the noise can be used as a modulation signal (specially
when it is heavily filtered) to create random cyclic variations.
On pre-cabled synthesizers, the noise module is either integrated into the oscillator, (its audio
output being placed as a complement on top of the wave form outputs) or the mixer directing
the signals to the filter. On the other hand, on modular synthesizers, it is an independent
module.
8.1.2 The filter or VCF
The audio signal generated by an oscillator (the wave form) is generally directed towards a
filter module (Voltage Controlled Filter). It is this module that allows the modeling of the sound
by filtering (by subtraction, explaining the name of this type of synthesis) the harmonics
situated around a cut-off frequency. It can be considered like a sophisticated equalizer, which
reduces, depending on the case, the low or high frequencies of a sound.
The removal of unwanted frequencies from a cut-off frequency is not sudden, but is done
progressively, depending on the filter slope. This filter slope is expressed in dB/octave. The
filters used in classic analog synthesizers have slopes of 24 dB/octave or 12 dB/octave.
The 24 dB/octave offers a more efficient filtering than the 12 dB/octave.